1. Field of the Invention
The present invention relates to video signal recorders and more particularly to digital video frame recorders used for buffering digital video signal data on a frame-by-frame basis.
2. Description of the Related Art
Digital video frame recorders are commonly used in color graphics display systems having high resolution. Such display systems typically have an input for accepting externally generated digital video data which is buffered on a frame-by-frame basis and displayed on a RGB video monitor. Often provided is an internal diagnostic capability whereby simple, digital video test data is generated internally for the purposes of performing self-diagnostic testing of specific electronic subsystems within the graphics display system. An internal computer or controller is used to control the generation and use of simple, digital video test data bit patterns and to put to appropriate use the results of such self-testing.
Examples of such color graphics display systems having self-diagnostic testing capabilities can be found in Irvin, U.S. Pat. No. 4,772,948 and Knierim, U.S. Pat. No. 4,780,755. Described therein are color graphics display systems having self-diagnostic testing capabilities for testing electronic subsystem elements within the overall display system.
One common test often performed on all types of video display systems is that where an externally generated "standard" video display test pattern signal, such as "color bars," is inputted and displayed. Aside from providing an indication as to how well the electronic subsystems within the graphics display system are performing, such a test also provides an indication as to how well the visual subsystem, i.e., the actual visual display device, such as a picture tube, is performing. Because the performance of the actual visual display device is being tested, this type of test requires some form of visual observation (e.g., actual observation by the human user, or an optical image processor). Thus, the simple, internal self-diagnostic testing capabilities such as those disclosed in the aforementioned patents will not suffice. Rather, externally generated video display test pattern signals must be inputted, displayed and observed.
To perform this test, the normal video input signal is removed or otherwise decoupled (e.g., by physically disconnecting the cable or other media carrying the signal). A video display test pattern signal generator, several of which are known in the art, is then coupled to the video input of the graphics display system to provide a video display test pattern signal. The video image representing the inputted video display test pattern signal is then displayed and observed on the display device of the display system. When the test has been completed, the video display test pattern signal generator is removed or otherwise decoupled and the normal video input signal is once again coupled to the video input of the display system.
Typically, video display test pattern signal generators supply video display test pattern signals as analog video signals using a large amount of analog circuitry, or as digital video signals using digital circuitry. If digital video signals are supplied, the display test pattern signal can be applied directly to the input of the graphics display system. However, if analog video signals are supplied, they must first be digitized by way of an analog-to-digital converter. In either case, switching circuitry external to the graphics display system must be provided to switch between the video display test pattern signal and the normal video input signal, or alternatively, the user must manually switch the media (e.g., cables) carrying the input signals.
Accordingly, it would be desirable to have a digital video frame recorder having a built-in capability to generate video display test pattern signals. It would be further desirable to have a digital video frame recorder which generated such video display test pattern signals in the digital format already used by its existing electronic subsystems. It would be still further desirable to provide such a video display test pattern signal generation capability by using already existing circuitry or hardware, or by adding only minimally thereto.